As communication demands increase, high speed optical transport systems are standardized. For example, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) Recommendation G.709 defines a technique of optical transport network (OTN) of approximately from 1.25 to 100 Gbps.
Related techniques are disclosed in Japanese Laid-open Patent Publication No. 11-308219 or Japanese Laid-open Patent Publication No. 2000-78153.